Various types of conveyances have been devised for transport of goods and people, which are changeable in form from one configuration, such as an operative uncollapsed or unfolded configuration, to a collapsed or folded configuration in which the overall dimensions of the conveyance are reduced. Examples of such devices include folding carts, folding bicycles, folding scooters, folding dollies, etc. The folding mechanics of such devices typically involve the use of one or more scissor joints of cross-members spanning between halves of the frame. This type of folding mechanism, as shown for example in U.S. Pat. Nos. 3,995,882; 4,045,051; 4,164,354 and 6,135,475, effectively enables collapse of the device to approximately one-half its unfolded size, in only one dimension such as side-to-side.
Folding wheelchairs are commonly constructed to bring the side frames together in order to accommodate the large diameter rear wheels. But the right and left side frames, with the associated large rear wheels, when folded together still occupy a relatively large volume of space. This type of folding configuration is not easily manageable for handling, storage or transporting in a vehicle such as an automobile, bus or aircraft or watercraft. It would be very desirable to have a portable conveyance which folds into a collapsed configuration which is smaller than the profile or volume of the side frame members or pieces of a conventional wheelchair.
A common type of folding chair which is now in wide recreational use has a simple seating support frame which has four pairs diagonally intersecting members when unfolded, and at least two upright members located at opposite corners at a rear of the frame. A recreational folding chair of this type is shown, for example, in U.S. Pat. No. 6,247,749, FIG. 1. In this type of frame, the ends of the diagonal frame members at the rear uprights must be free to travel upward along the length of the upright members in order for the frame to collapse into a generally columnar form. The '749 patent also discloses a similar frame with upright members at the front corners of the frame. But because the upright members do not extend above the seating surface, the diagonal side frame members cannot slide up the front upright members when the frame is folded. Therefore, the '749 patent describes front upright members which change in length by telescoping.
Attempts have been made to put wheels on these types of folding chair frames. U.S. Pat. No. 6,428,033 discloses a folding frame to which casters are attached. And U.S. Patent Application Publication No. US 2002/0084627 discloses a folding frame with telescoping front upright members and casters attached to the bottom of the frame. A separate foot rest is attached to the front of the frame. Because some sort of foot support is a necessity for a wheel chair, this presents a challenge to integrate the foot rest with a folding type frame without adding excessively to complexity and cost, and without interfering with the compactness of the chair in a folded configuration. Also, it is preferable for the foot rest to directly unfold with the opening up of the frame so that separate assembly, attachment or orientation of the foot rest is not required each time the chair is unfolded for use.